The invention relates to the detection of gas leaks and, more particularly, to a imaging system for producing a video display of leaks of invisible gas.
The transportation and storage of hazardous materials create a significant safety problem. Hazardous gases, in particular toxic or explosive gases, may be released to the environment. Often the gas is colorless and odorless, spreading as an invisible cloud, and creating difficult problems of location, containment and removal.
The natural gas industry, in particular, is concerned about the possible hazards of natural gas leaks at facilities and along transmission lines. Natural gas is a colorless odorless gas made up of 90 percent methane with ethane the next largest component. A natural gas detection system must be capable of leak detection along remotely located gas transmission lines, underground storage facilities, liquified natural gas (LNG) facilities, as well as mains and service lines of local gas distribution systems.
The Liquified Gaseous Fuels (LGF) Spill Effects Program at Lawrence Livermore National Laboratory has been studying the possible hazards associated with large scale spills of hazardous materials, focusing particularly on LNG vapor clouds. A variety of instrumentation has been tested including commercial hydrocarbon detectors, thermal imaging systems, Raman LIDAR systems, and fast response methane and ethane IR gas sensors capable of operating in a fog. Also studied were a commercial IR sensor, an IR helium neon laser absorption detector for methane, and a four band differential radiometer for detection of methane, ethane and propane. All these detection systems have been primarily directed towards the monitoring of large dense clouds of LNG vapors.
A passive infrared (IR) imaging system for use in monitoring LNG vapor cloud dispersion in vapor cloud combustion dynamics has been developed in the LGF program. The passive imaging system is a two wavelength broadband system which, when mounted in a helicopter and using the appropriate choice of interference filters, provides images of the dispersing gas cloud. The system utilizes a passive absorption technique, relying on the thermal radiation from the ground to produce a background image, and the absorption bands of methane, ethane and propane to attenuate the background image when the vapor cloud is present. The system demonstrated the ability to image a LNG vapor cloud from an altitude of 1 kilometer for gas concentrations down to 2-3 percent.
U.S. Pat. No. 3,317,730 discloses a method for determining atmospheric pollution by the detection of backscattered modulated infrared radiation.
U.S. Pat. No. 3,832,548 Wallack shows a general infrared absorption detector in which infrared radiation first passes through a filter means having a plurality of positions for transmitting selected wavelengths, and then passes through a sample cell to a detector.
U.S. Pat. No. 4,204,121 to Milly shows a mobile detector comprising a vertical sampling array for quantifying emission rates from pollution sources.
U.S. Pat. No. 4,264,209 to Brewster shows a system for producing an indication of a concentration of a gas of interest in which the gas is illuminated and the output is filtered alternately with two filters, one at an absorption band of a gas to be detected, the other at a passband outside the absorption band.
U.S. Pat. No. 4,262,199 to Bridges, et al., shows a mobile infrared target detection and recognition system including an assembly of infrared detection elements which scan a field of view to produce a signal representative of the infrared level from point to point.
U.S. Pat. No. 3,829,694 to Goto discloses apparatus for detecting gases or particles using Mie scattering of pulsed light beams to detect resonance absorption.
U.S. Pat. No. 3,517,190 to Astheimer discloses a method for monitoring stack effluent from a remote position by illuminating the effluent across a broad spectral band and detecting the reflected illumination in two spectral regions: one in an absorption band and one outside the absorption band to determine the quantity of absorbing gas from the signal ratio.
Thus, it is desirable to produce a mobile system to locate leaks of hazardous gas, particularly natural gas. A suitable system should not be easily confused by other sources, e.g., hydrocarbons from auto exhaust emissions. An airborne or mobile system is desired. A video imaging system would be highly advantageous since the operator can actually see where the leak is originating, thus eliminating the number of false alarms.
Accordingly, it is an object of the invention to provide a mobile remote detection (surface and/or airborne) system.
It is also an object of the invention to provide a video imaging system to locate hazardous gas leaks.
It is another object of the invention to provide a system which is simple to operate and interpret, e.g., operating in real time.
It is a further object of the invention to provide a detection system with a low false alarm rate.
It is a further object of the invention to provide a rugged, field reliable system.